Device with remote motor for controlling an aerodynamic control surface of a missile

ABSTRACT

An aircraft comprising at least one aerodynamic control surface ( 26 ) controlled using a remote motor ( 4 ), through a transmission comprising a linear device ( 7 ) rigid in torsion but flexible in bending and in tension and compression, to absorb thermomechanical deformations. This transmission comprises small clearances, good flexibility, does not require any additional support and makes favourable use of a reduction gear ( 9 ) located near the control surface ( 26 ) rather than near the motor ( 4 ).

The subject of this invention is a device with a remote motor for controlling an aerodynamic control surface of a missile.

Some aircraft and particularly missiles include control surfaces controlled by motors to change the flight direction. In the state of known art, the electric motor or other type of motor is coupled to the control surface through a reduction gear and/or a transmission element that may include control rods, levers or other elements, or devices for transformation of the rotating movement into a linear movement. The assembly is voluminous: the space available close to the control surface is sometimes insufficient to contain it. The motor then needs to be moved away to a remote location, for example in a fairing at a variable distance. In other cases, thermomechanical conditions make it impossible to place the motor close to the control surface, and such fairing is then used as thermal protection. The transmission then needs to be modified and extended.

Conventional embodiments then use combinations of control rods and levers, for which the performances may be insufficient: these embodiments are complex and heavy, and in particular they transmit high forces to the aircraft structure in more or less statically indeterminate arrangements that can apply forces to parts in bending. This is incompatible with mechanical deformations of the structure in flight in the case of missiles for which temperature rises are much greater than in other aircraft. Furthermore, the system will not operate correctly in practice unless parts are made flexible and unless functional clearances are added that reduce the precision of control and encourage the occurrence of vibrations.

Another difficulty specific to missiles and their high accelerations is based on vibrations applied to control surfaces. In some circumstances, particularly when bending and torsion modes are combined, resonance can appear that can destroy the control surfaces. The invention at least partially overcomes this risk by making control surface assemblies more rigid due to a particular arrangement of the transmission.

One solution to these difficulties is proposed with the invention. Apart from the motor and the aerodynamic control surface, the new device comprises a transmission extending between the two to communicate a movement to the control surface correlated to the motor rotation movement; it is innovative in that the transmission comprises mainly a linear device rigid in torsion but flexible in tension, compression and bending; the linear device is limited by a speed reduction gear between the linear device and the control surface and at least one sliding connecting element.

Prior art includes transmissions flexible in bending and rigid in torsion, usually in aircraft, to transmit rotation movements from a motor to a control surface or a series of remote control surfaces; but these transmissions do not have the flexibility in tension and compression necessary to absorb thermal expansions that occur in missiles.

If the reduction gear is placed close to the control surface instead of being adjacent to the motor as it usually is in known arrangements, vibrations are not transmitted to the linear device and the result is a more stable assembly of the control surface, which very much reduces the amplitude that the vibrations would reach if they propagated along the transmission towards the motor: the reduction gear acts as a mechanical filter.

One advantage of this transmission is that it does not need to be supported by the adjacent structure of the aircraft, it only transfers low forces to the adjacent structure, and it is not influenced by the deformations of the aircraft. The transmission can then be compact and perfectly statically determinate.

The transmission may also comprise a jack to convert the rotation movement into a translation movement, comprising a portion subject to the translation movement and articulated to a control lever of the control surface and a portion submitted to the rotation movement and coupled to the linear device. With this design, it becomes possible to benefit from conventional control surface construction techniques, in which the rotation movement is controlled by pressing on the lever.

The linear device may include shaft segments assembled together and through universal joints, for example three segments and two universal joints; it may also include a flexible shaft or any other equivalent means that those skilled in the art might envisage. The result with these two particular embodiments is satisfactory bending flexibility of the linear device.

The connecting elements with a sliding coupling may each include a grooved pin and bushing, which enable deformations of the device without applying the force on the linear device, the ends of which simply slide on the connecting elements.

The transmission may also include other parts such as bevel gears. A bevel gear may be arranged within the previous reduction gear if a movement conversion jack is used: in this case, the control surface control lever does not have to be in line with the linear device, which gives a much wider choice for the layout of the device.

The motor may be a brushless electric motor.

The invention will now be described and will be more easily understood considering its various aspects with reference to the following figures:

FIG. 1 is an overview of the device,

and FIGS. 2 and 3 show the arrangement of the device in a missile.

FIG. 1 shows the device according to the invention. A first motor module 1 is composed of a brushless electric motor 4, at the output of which there is a first bevel speed reduction gear 5 and an output shaft 6.

A second transmission module 2 is composed of a linear device 7, a bevel reduction gear 9 and a linear jack 10. The ends of the linear device 7 are connected to the output shaft 6 and to an input shaft 8 of the bevel reduction gear 9 by couplings 16 and 17 with a grooved shaft and bushing placed concentrically so that they can slide one in the other, while maintaining perfect transmission of the rotation movement.

The linear jack 10 comprises a ball screw 11 or a roller screw immobile in rotation and that moves in a nut 18 associated with a toothed wheel of the bevel reduction gear 9.

The device also includes a third reception module 3 comprising a control surface 26, a rotation shaft 14 of the control surface 26 and a drive lever 15 for said control surface 26. The lever 15 and the screw 11 are assembled by an articulation 13, and the reduction gear 9 is assembled free to rotate at a fixed point of the aircraft by another articulation 12. The linear device 7 is composed of successive segments 20, 21 and 22 attached to each other through two universal joints 23 and 24. It can also be formed from a single flexible shaft extending between the same ends and that can curve and straighten depending on deformations applied to it.

FIGS. 2 and 3 show a missile fitted with a fuselage 25 and four control surfaces 26 at the back, projecting radially outwards. A ramjet engine 27 occupies most of the section of the fuselage 25 at the control surfaces 26 and further forwards. The missile also comprises two external fairings 28 acting as air inlets and located behind two of the control surfaces 26.

The four motors 4 controlling the control surfaces 26 are placed in pairs in the two air inlet fairings 28. The motors that control the control surfaces 26 located in front of the air inlets 28 control them through an ordinary short transmission. The other control surfaces 26 are controlled according to the invention; the linear devices 7 extend in a portion of the annular space at a spacing of a quarter of a turn, between the fuselage 25 and the ramjet engine 27. The universal joints 23 and 24 curve the linear device 7 such that it remains near the centre of the annular space, with no support with the fuselage 25 or the wall of the ramjet engine 27. There are very easily adapted to displacements produced by thermomechanical deformations between the motor 4 and the control surfaces 26, by modifying the angles of the universal joints 23 and 24 and by sliding of the couplings 16 and 17 adjusting the transmission module 2 to match the variable distance between the motor module 1 and the receiving module 3. 

1. Device for controlling a missile aerodynamic control surface also comprising a motor element (1) performing a rotation movement and a transmission element (2) extending between the motor and the control surface (26) to transfer a movement correlated to the motor rotation movement to the control surface, device characterised in that the transmission element comprises a linear device (7) rigid in torsion, but flexible in tension, compression and bending, in that it comprises a reduction gear (9) located between the linear device and the control surface, and in that the linear device is limited by at least one sliding connecting element.
 2. Device for controlling a missile aerodynamic control surface according to claim 1, characterised in that the transmission element comprises a movement conversion jack (10) for converting the rotation movement into a translation movement, comprising a portion (11) subject to the translation movement and articulated to a lever (15) for controlling the control surface (26), and a portion (18) subject to the rotation movement and coupled to the linear device.
 3. Device for controlling a missile aerodynamic control surface according to claim 1, characterised in that the linear device comprises shaft segments (20, 21, 22) assembled together through universal joints (23, 24).
 4. Device for controlling a missile aerodynamic control surface according to claim 1, characterised in that the linear device comprises a flexible shaft.
 5. Device for controlling a missile aerodynamic control surface according to claim 1, characterised in that the sliding connecting element is a coupling with a grooved pin and bushing (16, 17).
 6. Device for controlling a missile aerodynamic control surface according to claim 1, characterised in that the reduction gear comprises an associated ball screw (11) and a nut (18) assembly.
 7. Device for controlling an aerodynamic control surface according to claim 2, characterised in that the reduction gear is a bevel reduction gear located between the jack (10) and the linear device (7).
 8. Device for controlling an aerodynamic control surface according to claim 1, characterised in that the motor is a brushless electric motor. 